The invention relates to evacuation devices.
If in a process chamber, or in any other vacuum chamber, pressures are supposed to be generated which lie in the high vacuum range (<=10−3 mbar), it is customary to use evacuation devices with a suction-side vacuum pump and an atmospheric pressure-side vacuum pump (backing vacuum pump). The suction-side vacuum pump is, as a rule, a mechanical, kinetic vacuum pump. Among these are gas ring vacuum pumps and turbo vacuum pumps (axial, radial) as well as molecular and turbomolecular vacuum pumps.
At pressures of said type the gases to be conveyed behave molecularly, that is, in such a way that a directed flow can only be achieved by pump structures which give the individual gas molecules pulses with a preferred direction, the desired direction. Since the gas molecules in the chamber to be evacuated have no preferred direction, only those gas molecules get into the suction nozzles of the connected vacuum pump which randomly have this direction of motion.
From U.S. Pat. No. 4,978,276, an evacuation device of the type relevant here is known. The rotor and stator of the mechanical-kinetic vacuum pump are formed to be cylindrical. In order to achieve the result that as many gas molecules as possible go into the suction nozzles of the vacuum pump connected to the chamber, i.e. the suction-side vacuum pump, the rotor has a conical hub whose diameter increases in the direction of the pressure side. The width of the webs between the hub and the cylindrical inner face of the stator decreases accordingly in the direction of the pressure side. This realization has the advantage that the inlet cross-section for the gases behaving molecularly, i.e. the suction-side annular surface in which the gases to be conveyed enter, is relatively large. An evacuation device of the known type is thus particularly suitable for those applications in which there is a demand for high gas throughputs.
The objective of the present invention is to further improve an evacuation device of the type relevant here with respect to the demand for high gas through puts.